The invention relates to a rotor for pressure sorters for sorting fibrous suspensions, such as those described and illustrated, for example, in U.S. Pat. Nos. 3,581,903, 3,849,302 and 4,155,841 or in EP No. 0 042 742-B1. Pressure sorters of this type have a rotationally symmetrical screen, mostly in the form of a screen cylinder, to which the fibrous suspension to be sorted is fed in the direction of the rotor axis, whereby the inner or outer side of the screen can form the inlet or inflow side of the screen. Mostly, the screen is arranged with a vertically oriented axis and the fibrous suspension to be sorted is supplied to the screen from above so that the upper end of the screen forms its inlet end. The rotor of this pressure sorter has a rotor axis coinciding with the screen axis and its operative regions rotate adjacent the inlet side of the screen. If the usable fibrous suspension flows through the screen from the inside to the outside, the rotor is arranged in the interior of the screen cylinder. If the inlet side of the screen is on the outside, the rotor has extending from its axis, a carrier which overlaps the screen wall and to which the regions of the rotor passing the outer side of the screen are attached. The invention does, however, also relate to those pressure sorters, in which the kinematic ratios are exactly the reverse, i.e. in which a screen rotating about its axis and a stationary "rotor" are provided.
The rotor of such a pressure sorter has the object of preventing the screen apertures from becoming clogged by fiber conglomerates or by impurities contained in the fibrous suspension. For this purpose, the rotor bears adjacent the screen inlet side cleaning elements which move through the fibrous suspension to be sorted and are designed such that they generate positive pressure surges in the fibrous suspension on their leading side and negative pressure surges on their rear side which, again, bring about flows flushing through and flushing back through the screen apertures. In some of the known pressure sorters according to the publications cited in the aforesaid, measures have been taken in addition to generate turbulences in the fibrous suspension to be sorted at the screen inlet side. These turbulences are intended to prevent the formation of a fibrous fleece in the fibrous suspension to be sorted at the inlet side of the screen. For this purpose, the known cited pressure sorters are provided at the screen inlet side with strips placed on the screen or grooves worked into the screen which extend parallel to the rotor axis, or recesses are worked into the screen wall at the screen inlet side in the region of the screen apertures. This unevenness at the screen inlet side generates the desired turbulences in the fibrous suspension to be sorted since the fibrous suspension to be sorted flows helically along at the screen inlet side as a result of the rotating rotor. These turbulences counteract the formation of any fibrous fleece and they also have the effect that the circulating fibrous suspension which has been thickened to a great extent at the screen inlet side due to fractionation is broken up such that a larger portion of the usable fibers can pass through the screen apertures. Screens having strips placed thereon or grooves worked therein are, however, subject to quite considerable great wear and tear, above all during sorting of fibrous suspensions recovered from mixed waste paper or the like which contain a considerable proportion of solid impurities which lead to rapid wear and tear on the edges of the strips and grooves. Moreover, these screens are expensive to manufacture. This also applies for screens, in which recesses are worked into the screen wall in the region of the screen apertures from the side of the screen inlet.
It is obvious that these comments also apply for those pressure sorters in which the screen is caused to rotate and the cleaning elements are stationary.
The rotors of the known pressure sorters have either a set of arms attached to a central rotor shaft and strip-like cleaning vanes as cleaning elements, which are attached to the outer ends of these arms, or the rotor has a circular-cylindrical casing with cleaning elements attached to the side facing the screen, these cleaning elements having, like the strip-like cleaning vanes mentioned above, a profile which is in cross section transverse to the rotor axis similar to an airfoil. In the latter case, the cleaning elements can also be strip-like cleaning vanes. However, rotors having a circular-cylindrical casing are also known, to which short vane pieces are attached as cleaning elements to avoid pulsations in the fibrous suspension containing usable fibers, the so-called accepted material, leaving the pressure sorter.